Fixing trace on a motor PCB

Discussion in 'General Electronics Chat' started by Sam Matthews, Jun 15, 2016.

  1. Sam Matthews

    Thread Starter Member

    Jan 16, 2016
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    I have a motor board out of a dyson vacuum hoover that controls the brush motor in the head, which is a 240VDC motor. The board is powered via 240VAC and converts through the typical bridge rectification method of 4 diodes. It appears to have a 400v 100uF capacitor to smooth this rectified voltage out. My issue is that there is a broken trace between a small capacitor and a resistor, and this is causing my motor not to work.

    The question i'm asking is; is it safe to solder a wire to bridge this breakage?

    I have had the board unplugged for 24hours, how long would you say this capacitor would take to discharge, or would it not need to discharge for it to be safe to bridge this break with a soldered wire?
     
  2. dl324

    Distinguished Member

    Mar 30, 2015
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    Just make sure the wire is sized to handle the current.

    To be safe, short the cap terminals to move sure it's discharged.
     
  3. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Normally if you scrape clean any PCCT board protection down to the solder or copper of the trace and tin it and solder a copper wire bridge on each trace.
    If unsure of any capacitor, just short it with the power off, but 24hrs seems a reasonable time for a small cap to self discharge.
    Are you sure that is not the Chinese knock-off version, DieSoon?:)

    Max.
     
    Tonyr1084 and KeepItSimpleStupid like this.
  4. #12

    Expert

    Nov 30, 2010
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    Bridging burnt circuit board traces is a necessary skill, not an uncertain kludge with unpredictable results. It's just a tool that every technician is supposed to know.
     
  5. Sam Matthews

    Thread Starter Member

    Jan 16, 2016
    178
    3
    So if i just short the cap out, with a wire or with a resistor?

    The trace thats broken is very thin, however i will use something substantial to handle the current from the 240v motor.

    I know this is some basic principles but i just wanted to double check i was safe to put the soldering iron to the copper with this capacitor on board after AC power.
     
  6. debe

    Well-Known Member

    Sep 21, 2010
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    Max, you will find Dyson shifted manufacturing to China quite some time ago ( cheep labour but still an expensive product)
     
  7. dl324

    Distinguished Member

    Mar 30, 2015
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    That's unfortunate. I bought one about ten years ago and it still works well. Prior to that, I was buying a new vacuum every few years because they weren't cost effective to repair.
     
  8. Sam Matthews

    Thread Starter Member

    Jan 16, 2016
    178
    3
    Thank you guys, i really appreciate the help and support, not to mention the knowledge everyone has around here!
     
  9. Sam Matthews

    Thread Starter Member

    Jan 16, 2016
    178
    3
    Let me just clarify this, i'm supposed to be shorting the cap leads together to discharge it, right?
     
  10. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Yes, but by this time a 100μf it should be fully discharged!
    And that value is not very large if it were for smoothing a motor supply.
    Is it a P.M. motor, BTW?
    Max.
     
  11. Sam Matthews

    Thread Starter Member

    Jan 16, 2016
    178
    3
    I can't find much detail regarding the motor, only one datasheet. I've attached it to this message.

    Also, i shorted the cap leads together, and the lead i used ended up flying across the room with a bang and a spark.
     
  12. dl324

    Distinguished Member

    Mar 30, 2015
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    Better safe than sorry, short it again.
     
  13. Sam Matthews

    Thread Starter Member

    Jan 16, 2016
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    You best not be trolling me here. I feel i may be left with no hands left at some point at this rate.
     
  14. dl324

    Distinguished Member

    Mar 30, 2015
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    Completely serious. Any voltage remaining will be less than the first attempt, so the lead shouldn't fly out of your hands this time.
     
  15. Sam Matthews

    Thread Starter Member

    Jan 16, 2016
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    I, for some reason, didn't expect this to happen and it scared the living day lights out of me.
     
  16. dl324

    Distinguished Member

    Mar 30, 2015
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    When I was in college, some jokers liked to charge caps and put them back in the storage drawers hoping to zap some unsuspecting classmate or instructor... But they weren't working with high voltages.
     
  17. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Surprised it was still charged that much, I have blown a hole in the ends off a few screw drivers in my time!:(
    Max.
     
  18. Sam Matthews

    Thread Starter Member

    Jan 16, 2016
    178
    3
    The lead is burnt and the cap lead has a little chunk missing >.< - So, back to the fault at hand. It seems the break in the pcb was not the issue after all...

    I'm attempting to repair a AC/DC Motor board. What confuses me here though is that the board holds a MCU. Why on earth would such a board have a MCU on there? The board doesn't need to do any switching from my knowledge, the switching is done elsewhere on the vacuum hoover.
     
  19. MaxHeadRoom

    Expert

    Jul 18, 2013
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    If the motor controls the rollers etc, are they are variable speed?
    You did not mention the original symptom, if the motor does not turn, try it on a low voltage supply, it does not appear very large, as a last resort, try an automotive battery, it should run around 100rpm at least.
    Can you post a pic of the board?
    Max.
     
  20. Sam Matthews

    Thread Starter Member

    Jan 16, 2016
    178
    3
    I doubt its a variable speed enabled if i'm honest. But i'm more than likely incorrect.

    I will attempt attaching this motor to a 12v source, thats as high as i have though. Not sure if it will spin.

    image.jpg image.jpg
     
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